A sizing composition, or chemical treatment, is generally applied to all glass fibers shortly after they have been formed, as a means to protect the glass fibers from breaking and marring during processing. As used herein, glass fibers collectively refers to continuous glass fiber filaments formed by the attenuation of a stream, or streams, of molten glass to strands formed when continuous glass fibers filaments are gathered together.
Glass fibers are useful in providing reinforcement for polymeric resin materials used in forming fiber-reinforced plastics (FRPs). The glass fibers provide dimensional stability to the polymeric materials, due to their high tensile strength, heat resistance and moisture resistance. In addition to protecting the glass fiber during manufacture, the sizing composition improves the compatibility of the glass fibers with matrix resins.
One measure of compatibility, or incompatibility, between the glass fiber and resin matrix is the existence of so called white glass. By “white glass”, as used herein is meant that in a clear fiberglass reinforced resin sheet, when laid on a black background, white fiberglass strands can be seen. The showing of white glass indicates a lack of contact between the sized glass fibers and the resin. This lack of contact generally leads to a lower strength panel.
The sizing of glass fibers which are used to reinforce plastic resin matrices is well known. For instance, U.S. Pat. No. 3,997,306 discloses glass fiber size which contains a phenolic epoxy resin, the reaction product of the partial ester of a polycarboxylic acid containing one or more unesterified carboxyl groups with a compound containing more than one epoxy group, an amino silane coupling agent, a methacryloxy alkyl trialkoxy silane, and a non-ionic surface active agent.
U.S. Pat. No. 4,126,729 discloses gun roving glass fibers coated with an aqueous-based size comprising an epoxidized polyvinyl acetate copolymer in combination with a vinyl acetate-ethylene copolymer and a vinyl acetate copolymer.
U.S. Pat. No. 4,457,970 discloses treated glass fiber strands have on the glass an aqueous treating composition or a dried residue thereof. The treating composition has a vinyl-containing coupling agent, an epoxidized thermoplastic polymer or copolymer, an organo-reactable silane coupling agent in an unhydrolyzed and/or partially hydrolyzed condition or an interaction product of the epoxidized polymer or copolymer and organo-reactable silane coupling agent, and a glass fiber lubricant. U.S. Pat. No. 4,789,593 discloses glass fibers treated with an aqueous chemical treating composition having a polar thermoplastic film-forming polymer, coupling agent and lubricant. The aqueous emulsion of the thermoplastic film-forming polymer has an average amount of aliphatic unsaturation of less than around 1.5 aliphatic double bonds/mole of polymer and has a ratio of aliphatic unsaturation to aromatic unsaturation not to exceed 0.1.
U.S. Pat. Nos. 5,491,182 and 5,665,470 describe sizing compositions in which the average molecular weight of the polymer is less than 55,000. The polymer sizing composition could be formed from any number of different monomers including examples containing glycidyl methacrylate and hydroxypropyl acrylate. The patent solved the problem of improving the clarity of an FRP, especially in acrylic resins.
U.S. patent application Ser. No. 10/283,406 describes fiberglass copolymer binders containing both acid and hydroxyl functionality. The binders are further crosslinked to form a continuous bonded mess of glass fibers, or fiberglass.
It is desirable to have sizing compositions which provide very good compatibility between the glass fibers and polymer matrices used in forming reinforced plastics.
Surprisingly it has been found that a sizing composition having a copolymer binder containing phenyl, hydroxy, or alkoxy functionality increases the compatibility between glass fiber and resin matrix, as seen by a reduction in white glass.